The present invention relates generally to hydraulic fluids, and more particularly, to hydraulic fluids that have fire resistant properties.
Hydraulic fluids are fluids which are used to offer resistance in hydraulically operated mechanisms. The main classes of hydraulic fluids commonly used are petroleum-based [See U.S. Pat. Nos. 4,566,994 and 4,800,030] (composed of chemically saturated or unsaturated, straight-chained, branched or ring-type hydrocarbons [See U.S. Pat. No. 5,236,610]), water/glycol solutions, and water-in-oil emulsions [See U.S. Pat. No. 3,236,778].
There are several notable disadvantages to these conventional types of hydraulic fluids. The petroleum-based hydraulic fluids pose certain environmental and health risks. In addition, petroleum oils may be the least fire-resistant and attempts to improve fire-resistance by the addition of fire-resistant compounds tends to reduce lubricity. Petroleum is a non-renewable and limited natural resource. Moreover, petroleum oil allowed to escape into the ground causes soil and groundwater contamination which can pose additional health and environmental problems.
Water-based hydraulic fluids have disadvantages as well. Hydraulic fluids of this type often lack sufficient mechanical stability and lubricity to operate at high temperatures and pressures.
There is a need for hydraulic fluids which are based on renewable natural resources and which simultaneously have the characteristics of desirable viscosity, lubricity, stability, and volatility while reducing potential harm to the environment.
In one aspect, the present invention provides a hydraulic fluid composition comprised of a mixture of about 20% to about 90% by weight of a trialkoxyalkyl-phosphate, about 10% to about 80% by weight of a natural triglyceride diluent, and about 0.1% to about 2% by weight of a high molecular weight polymer. In a preferred embodiment, the trialkoxyalkyl-phosphate is tributoxyethyl-phosphate and the natural triglyceride diluent is canola oil.
In another aspect, the present invention provides a hydraulic fluid composition comprised of a mixture of about 20% to about 90% by weight of a trialkoxyalkyl-phosphate, about 10% to about 80% by weight of a synthetic ester diluent, and about 0.1% to about 2% by weight of a high molecular weight polymer. In a preferred embodiment, the trialkoxyalkyl-phosphate is tributoxyethyl-phosphate and the synthetic ester diluent is selected from the group consisting of polyol esters of C6-C18 acids and dibasic acid esters of monohydric alcohols.
In a further aspect, the present invention provides a hydraulic fluid composition comprised of a mixture of about 20% to about 90% by weight of a trialkoxyalkyl-phosphate, about 10% to about 80% by weight of a polypropylene glycol diluent, and about 0.1% to about 2% by weight of a high molecular weight polymer. In a preferred embodiment, the trialkoxyalkyl-phosphate is tributoxyethyl-phosphate and the polypropylene glycol diluent is selected from the group consisting of polypropylene glycols of the general formula:
R1Oxe2x80x94[CH2xe2x80x94CH(CH3)xe2x80x94O]nxe2x80x94R2
where R1 and R2 are independently selected from the group consisting of H, an alkyl, alkenyl, and alkadienyl chains of from 1 to 18 carbons and n=3-40.
In yet another aspect, the invention provides for the optional addition to any of the above-described hydraulic fluids of at least one compound selected from the following groups: about 0.5% to about 5% by weight antioxidant, about 0.1% to about 2% by weight corrosion inhibitor, about 0% to about 2% by weight antiwear agent, and about 0% to about 10% by weight viscosity modifier.
Further objects, features, and advantages of the present invention will become apparent from the detailed description of the invention and the preferred embodiments that follows.
The present invention provides novel fire-resistant hydraulic fluid compositions. One such fluid contains a mixture of a trialkoxyalkyl-phosphate and a natural triglyceride diluent. Another hydraulic fluid of the invention contains a mixture of a trialkoxyalkyl-phosphate and a synthetic ester diluent. Still other fluids of the invention contain a trialkoxyalkyl-phosphate and mixtures of both a natural triglyceride and a synthetic ester. Still another hydraulic fluid of the invention contains a mixture of a trialkoxyalkyl-phosphate and a polypropylene glycol diluent. Yet another hydraulic fluid of the invention contains a trialkoxyalkyl-phosphate and a mixture of a synthetic ester and a polypropylene glycol diluent. Another hydraulic fluid of the invention contains a trialkoxyalkyl-phosphate and a mixture of a natural triglyceride and a polypropylene glycol diluent. In still another hydraulic fluid of the invention, a trialkoxyalkyl-phosphate is mixed with a diluent comprised of a mixture of a natural triglyceride, a synthetic ester, and a polypropylene glycol. Desirably, these compositions also contain a high molecular weight polymer, as defined herein.
The inventors have found that the use of the hydraulic fluid compositions of the present invention improves fire resistance. As used herein, xe2x80x9cfire resistancexe2x80x9d refers to the ability of a fluid to pass the flame propagation and hot surface ignition tests described below in Example 7. The hydraulic fluid compositions also have a lower heat of combustion compared to hydraulic fluids lacking phosphate esters. See, e.g., Table II of Example 1.
Hydraulic fluids of the present invention contain between about 20% to about 90% by weight of a trialkoxyalkyl-phosphate. Trialkoxyalkyl-phosphates may be represented by the general formula: (R3xe2x80x94O)3P=O where R3 is (CnH2n+1xe2x80x94Oxe2x80x94CmH2m+1) where n is between 1 and 18 and m is between 2 and 6. These trialkoxyalkyl-phosphates are further characterized as having a high flash point and a low heat of combustion, and as being nontoxic and environmentally acceptable. In a preferred embodiment, the trialkoxyalkyl-phosphate is tributoxyethyl-phosphate. However, any trialkoxyalkyl-phosphate of the above formula may readily be incorporated in the compositions of the present invention.
The preferred hydraulic fluids of the invention also may contain between about 10% to about 80% of a natural triglyceride as a diluent. The natural triglycerides used in the hydraulic fluid compositions of the present invention are glycerol esters of fatty acids, and the chemical structure of these esters can be defined by the following formula: 
wherein R4, R5, and R6 can be the same or different and are selected from the group consisting of saturated and unsaturated straight-chained alkyl, alkenyl, and alkadienyl chains of 9 to 22 carbon atoms. These triglycerides are further characterized by having a high flash point (over 500xc2x0 F. C.O.C.). As defined herein xe2x80x9cC.O.C.xe2x80x9d refers to the Cleveland Open Cup test, a standard measurement of flash point.
Several modified versions of these natural triglycerides may be included in the hydraulic fluids of the present invention. Such modifications may be made in the natural triglycerides by oxidation, polymerization, hydrogenation, and transesterification thereof.
Conventional animal fats and vegetable oils provide a convenient source for the natural triglyceride diluents useful in the invention. In a preferred embodiment, the vegetable oil is canola oil. Other suitable vegetable oils include corn oil, cottonseed oil, sunflower oil, peanut oil, soybean oil, coconut oil, Jojoba oil, castor oil, palm oil, and palm kernel oil. These natural triglycerides are readily available from commercial sources, including, for example, Calgene, Inc., Pfau, Inc., Acme Hardestry, Inc., and Resource Material Corp.
These natural triglycerides have numerous properties which are advantageous in hydraulic fluids. The use of natural triglycerides as diluents in hydraulic fluids confers the benefit of a low cost, renewable, natural resource which is environmentally acceptable in contrast to conventional petroleum-based hydraulic fluids. Natural triglycerides possess a greater viscosity stability at varying temperatures compared to mineral oil (petroleum-based) products. The structure of triglycerides is apparently equally stable against mechanical stresses in hydraulic pumps than mineral oil-based fluids when compounded properly. In addition, due to the polarity of triglycerides, it is expected that their ability to adhere to metal surfaces provides superior lubricity. Triglyceride-based hydraulic fluids also have a lower heat of combustion than conventional petroleum-based hydraulic fluids. The fire and flash points of triglycerides are clearly higher than that of hydrocarbon basic oils.
Given these guidelines, one of skill in the art could readily select other natural triglycerides to be included in the hydraulic fluid compositions of the present invention.
Another embodiment of the hydraulic fluid compositions of the present invention contains a synthetic ester as the diluent component. The synthetic ester diluent is selected from the group consisting of polyol esters of C6-C18 acids and dibasic acid esters of monohydric alcohols. These synthetic esters may be derived from polyhydric alcohols reacted with monobasic acids or polybasic acids reacted with monohydric alcohols. In a preferred embodiment, the synthetic ester may be diisononyl phthalate. In another preferred embodiment, the synthetic ester may be a pentaerythritol ester mixture of capric and caprylic acids. One suitable commercially available pentaerythritol ester is available from the Stepan Chemical Corporation under the trademark Kesco 874(trademark). Other synthetic esters may also be commercially obtained.
The synthetic ester may be used in place of, or as a supplement to, the natural triglycerides. When used as the sole diluent, the synthetic ester is present in amounts of about 10% to about 80% by weight. When used to supplement the natural triglycerides, the synthetic ester may be present in amounts of about 15% to about 30% by weight and the triglyceride in amounts of 40% to about 60% by weight.
Another embodiment of the hydraulic fluid compositions of the present invention contains polypropylene glycol as the diluent component. In a preferred embodiment, the polypropylene glycol diluent is selected from the group consisting of polypropylene glycols of the general formula:
R1Oxe2x80x94[CH2xe2x80x94CH(CH3)xe2x80x94O]nxe2x80x94R2
where R1 and R2 are independently selected from the group consisting of H, an alkyl, alkenyl, and alkadienyl chains of from 1 to 18 carbons in length and n=3-40. One such commercially available polypropylene glycol is manufactured by the Union Carbide Corporation under the trademark UCON LB-625(trademark). The polypropylene glycol constituent provides the present hydraulic fluid compositions with a low heat of combustion, high lubricity, and high hydrolytic and thermal stability.
The polypropylene glycol may be used in place of, or as a supplement to, the natural triglycerides. In addition, the polypropylene glycol may be used either alone or in combination with the synthetic esters described above. Another embodiment of the hydraulic fluid compositions contains as the diluent a mixture of a natural triglyceride as described above, a synthetic ester, and a polypropylene glycol. When used as the sole diluent, the polypropylene glycol is present in amounts of about 10% to about 80% by weight. When used to supplement the natural triglycerides, the polypropylene glycol may be present in amounts of about 15% to about 30% by weight and the triglyceride in amounts of 40% to about 60% by weight.
The hydraulic fluids of this invention also contain between about 0.1% to about 2% by weight of a high molecular weight polymer soluble in the selected diluent. As used herein, xe2x80x9chigh molecular weightxe2x80x9d refers to polymers having a molecular weight of at least 50,000. The incorporation of high molecular weight polymers improves fire resistance of the hydraulic fluid compositions of the present invention. Particularly desirable are polymers selected from the group consisting of polystyrene, styrene-butadiene copolymers, polyesters, polymethacrylates, polyvinyl acetate, and vinyl chloride acetate copolymers. These polymers are commercially available, such as the styrene butadiene copolymer manufactured by the Lubrizol Corporation under the trademark Lubrizol 5994(trademark). In a preferred embodiment, the high molecular weight polymer is selected from the group consisting of a mixture of methyl methacrylate and n-butyl methacrylate resin, a mixture of vinyl chloride, vinyl acetate, and vinyl alcohol terpolymer, and a copolymer of styrene and maleic anhydride. These polymers are also commercially available, e.g., a methyl methacrylate and n-butyl methacrylate resin mixture manufactured by the Degussa Corporation under the trademark Degalan LP-62/05(trademark), and a copolymer of styrene and maleic anhydride manufactured by the Monsanto Corporation under the trademark Scripset 520(trademark) resin. Other polymers soluble in the diluent constituent may readily be included by one of skill in the art.
Optionally, other conventional hydraulic fluid components may be added to the hydraulic fluid compositions of the present invention. Such optional components include, for example, antioxidants, corrosion inhibitors, antiwear agents, and viscosity modifiers.
Antioxidants are useful additives for preventing the degradation of the hydraulic fluid through oxidation. Antioxidants are desirably present in the hydraulic fluids in the amount of about 0.5% to about 5% by weight. Such antioxidants may be selected from the group consisting of aromatic amine, quinoline, and phenolic compounds. One such antioxidant which is commercially available is an alkylated diphenyl amine produced by the Vanderbilt Corporation under the trademark Vanlube NA(trademark). Although polymerized trimethyl-dihydro-quinoline (commercially available from the Vanderbilt Corporation under the trademark Vanlube RD(trademark)) and 4,4xe2x80x2-methylene bis(2,6-di-tert-butylphenol) are preferred, other antioxidants may be readily selected by one of skill in the art.
Suitable corrosion inhibitors for both ferrous and non-ferrous metals may be selected from the battery of conventional corrosion inhibitors used in the industry. Corrosion inhibitors are desirably present in the hydraulic fluid compositions of the present invention in the amount of about 0.1% to about 2% by weight. A preferred corrosion inhibitor is tolyltriazole, however, other known and commercially available corrosion inhibitors could readily be used by one of skill in the art.
Similarly, numerous antiwear agents or lubricants are known in industry. Antiwear agents are optionally present in the hydraulic fluids of the present invention in the amount of about 0% to about 2% by weight. Preferred antiwear agents used in the hydraulic fluid compositions are selected from the group consisting of an amine phosphate which results from the reaction of mono and di-hexyl phosphate with C11-C14 branched alkyl amines. One such commercially available antiwear agent is produced by the Ciba-Geigy Corporation under the trademark Irgalube 349(trademark). One of skill in the art could readily include other suitable phosphorous and sulfur based antiwear agents.
Conventional viscosity modifiers may optionally be included in the hydraulic fluid compositions of the present invention. Viscosity modifiers are optionally present in the hydraulic fluid compositions in the amount to about 0% to about 10% by weight. A viscosity modifier selected from the group consisting of a dimer acid ester and polymerized vegetable oil is preferred. One suitable commercially available viscosity modifier is a dimer acid ester available from Unichema International, Inc. under the trademark Priolube 3986(trademark). Other such modifiers may be selected by one of skill in the art.